Lubricant Additives Research Articles

Nanostructured lubricant additives for titanium alloy: Lubrication by the solid-liquid interface with Coulomb repulsion

In this work, the advantage of Coulomb repulsion in the intermolecular forces experienced by molecules on the solid-liquid nanosized contact interface is taken, and the superior friction-reducing property of Cu3(PO4)2·3H2O (CuP) oil-based additives has been confirmed for titanium alloy. Three-dimensional (3D) CuP nanoflowers (CuP-Fs) with a strong capillary absorption effect are prepared to achieve the homogeneous mixing of solid CuP and lubricating oil. Lubrication by CuP-Fs additives for titanium alloy, friction coefficient (COF) can be reduced by 73.68%, and wear rate (WR) reduced by 99.69%. It is demonstrated that the extraordinary friction-reducing property is due to the repulsive solid-liquid interface with low viscous shear force originating from Coulomb repulsion between polar water molecules in CuP and non-polar oil molecules. However, any steric hindrance or connection between this repulsive solid-liquid interface will trigger the adhesion and increase the viscous shear force, for example, dispersant, hydrogen bondings, and shaky adsorbed water molecules. Besides, the lamellar thickness of CuP and the molecular size of lubricant both have a great influence on tribological properties. Here the lubrication mechanism based on interface Coulomb repulsion is proposed that may help broaden the scope of the exploration in low-friction nanomaterial design and new lubricant systems.

A Review on the Impact of Bio-Additives on Tribological Behavior of Diesel Fuels

Automobile engines require lubrication to lessen the impact of friction due to the high levels of wear and frictional heat generated by the sliding parts. Wear and friction will cause engine parts to endure for less time, be less reliable, and require more maintenance. Diesel fuel can potentially be replaced with biodiesel among other fuels. Diesel engines have a serious problem with equipment that is lubricated by the fuel itself. This study’s goal is to assess the influence of bio-additives on the diesel fuel tribological behavior and energy balance during the car’s idle running, acceleration, constant speed, and braking. Lubricity issues with reformulated diesel and lubricity test procedures are explained. The relationship between tribology and bio-additives is also briefly illustrated. According to the literature, adding bio-additives to fuel boosts its lubricity. Biodiesel has long been considered an additive with excellent lubricant properties. Even in small amounts, adding biodiesel to diesel fuel can increase its lubricity without the need for conventional lubricity additives. This is especially true for diesel fuel with ultralow sulfur. Diesel fuel characteristics determine the precise blending percentage needed to provide the proper lubricity of maximum 520 μm testing wear scars with a high-frequency reciprocating rig (HFRR), although 2% biodiesel nearly invariably imparts adequate lubricity to biodiesel blends. Tall oil fatty acid (TOFA) was one of the bio-additives investigated by HFRR. When the additive concentration was raised from 0 to 500 g/g, the wear scar diameter (WSD) of nonadditive diesel fuel was lowered by 60.3%, from 630 to 250 μm, and the coefficient of friction (COF) was lowered by 95.7%, from 0.47 to 0.02.

Performance of inert particles as lubricant additives compared to fully formulated industrial forming oils in sheet metal forming

The increasingly restrictive legislation on the use of hazardous chemicals in lubricant formulation necessitates the use of less hazardous lubricant additives in the sheet metal forming industry. The tribological performance of calcium carbonate (CaCO3) as a green lubricant additive was evaluated in comparison to commercially available forming lubricants used in industry, some of which contain hazardous chemicals such as chlorinated paraffins to enable their function. The lubricants were tested by four-ball wear testing, four-ball weld load testing, and bending-under-tension. The ease of cleaning of surfaces formed with the different lubricants was evaluated by methods used in industry and the viscosity was evaluated using standard methods. The CaCO3 mixtures showed a better performance than commercial lubricants in four-ball wear testing, worse performance in four-ball weld load testing, worse cleanability, and a similar development of drawing force in bending-under-tension over 1000 consecutive strokes. When added to fully formed commercial lubricants, the particles degrade the performance of the lubricant in resisting adhesive wear but improve its capacity for resisting abrasive wear. Surfaces of formed parts after bending-under-tension testing with CaCO3 mixtures were scratched, while parts formed using commercial lubricants showed less scratching. The effect of including particles in a commercial lubricant depended on the application, either degrading it or improving it. It is therefore clear that the use of solid particles as lubricant additives should be constrained to selected applications where abrasive wear is a dominant wear mechanism.

Hydrophilized MoS2 as Lubricant Additive

Molybdenum disulfide (MoS2) has been used in a variety of lubrication products due to its highly tunable surface chemistry. However, the performance of MoS2-derived tribofilms falls short when compared to other commercially available antiwear additives. The primary objective of this study is to improve the tribological performance of MoS2 as an additive for lithium-based greases. This was achieved by functionalizing the particle with hydrophilic molecules, such as urea. Experimental results indicate that the urea-functionalized MoS2 (U-MoS2) leads to a notable decrease in the coefficient of friction of 22% and a substantial reduction in the wear rate of 85% compared to its unmodified state. These results are correlated with the density functional theory (DFT) calculation of U-MoS2 to theorize two mechanisms that explain the improved performance. Urea has the capability to reside both on the surface of MoS2 and within its interlayer spacing. Weakened van der Waals forces due to interlayer expansion and the hydrophilicity of the functionalized U-MoS2 surface are catalysts for both friction reduction and the longevity of tribofilms on hydrophilic steel surfaces. These findings offer valuable insights into the development of a novel class of lubricant additives using functionalized hydrophilic molecules.

Investigation of NR, BR, and SBR composite material properties and internal mixer Wear under various lubricating oil media during mixing process

During the blending process, the choice of lubricant used in the internal mixer significantly affects the properties of composite materials. This study thoroughly investigates the mechanisms that enhance the mechanical properties and anti-wear characteristics of Natural Rubber/ Butadiene Rubber/Solution-Polymerized Styrene Butadiene Rubber composite materials by employing both commonly used lubricants and graphene-based lubricant mediums. The research offers data-driven insights to enhance material performance during internal mixer blending and protect the end-face metals. The incorporation of graphene as a lubricant additive results in its deposition on friction pair surfaces, forming a protective anti-wear layer that prevents direct contact between the friction pairs and effectively reduces wear.Throughout the blending process, the composite materials inevitably come into contact with the lubricant. This research reveals that the addition of lubricant improves the dispersion of SiO2 particles while reducing aggregate formation. Consequently, the SiO2 particles-TESPT-rubber crosslinking network becomes denser, significantly enhancing the performance of Natural Rubber/ Butadiene Rubber/Solution-Polymerized Styrene Butadiene Rubber composite materials. Specifically, when using commonly used lubricant mediums, the material's hardness, tensile strength, and tear strength increase by 0.88 %, 7.8 %, and 4.5 %, respectively. In contrast, under the graphene lubricant medium, these properties improve by 2.7 %, 16.8 %, and 24.9 %, respectively. Notably, Natural Rubber/ Butadiene Rubber/Solution-Polymerized Styrene Butadiene Rubber composite materials using the graphene lubricant medium experience substantial reductions in rolling resistance and improved anti-wet skid performance.When comparing Natural Rubber/ Butadiene Rubber/Solution-Polymerized Styrene Butadiene Rubber composite materials with and without lubricants, composites prepared with both commonly used lubricants and graphene lubricants show significant reductions in metal wear and changes in metal surface roughness. Metal wear decreases by 17.5 % and 28.7 %, respectively, while changes in metal surface roughness are reduced by 46.3 % and 68.7 %, respectively.

Extreme pressure and anti-wear properties of polycarboxylate superplasticizer modified 3D porous graphene/SiO2 as water-based lubricant additives

Lubricants can effectively solve the large amount of energy loss and environmental pollution caused by frictional wear. Graphene-based materials water-based lubricants have attracted attention due to their excellent various properties. But their application is still hindered by many obstacles. In this paper, a novel polycarboxylate superplasticizer modified 3D porous graphene/SiO2 (PG/SiO2) nanomaterial was prepared as water-based lubrication additives. The base fluid with good cooling properties was obtained by adding Kunlun full synthetic grinding/cutting fluid to deionized water and diluting it to 5% by weight. It is found that PG/SiO2 had a good synergistic effect, which could effectively improve the extreme pressure performance (PB/PD), with the maximum improvement rates of 39.7% and 86.3%, respectively. Meanwhile, significantly enhance the friction reduction (35%) and anti-wear (72.2%) properties of the base fluid. The enhancement mechanism was revealed by experimental and characterization analysis. Due to the excellent mechanical properties of graphene itself and synergistic effects including the rolling bearing effect of PG/SiO2 and the buffering effect of SiO2 in its intercalation, the PG/SiO2 nanomaterials can significantly improve the extreme pressure performance of the base fluid. Further, theoretical calculations revealed the enhancement effects of the long chains of the polycarboxylate superplasticizer on the dispersibility and surface adsorption of graphene, and the modified graphene on the diffusive movement of water molecules.

The role of epoxidation process on improving the oxidative, thermal stability, and tribological performance of mustard oil nano lubricants

This study investigated the potential of inedible mustard oil (MO) (Brassica juncea) as a suitable bio-lubricant for enhanced thermal, oxidative stability, and tribological performance. To improve the MO's oxidative stability, it was subjected to a chemical epoxidation reaction, forming epoxidized mustard oil (EMO). The MO and EMO were evaluated for viscosity, functional groups, wettability, oxidative stability, thermal stability, friction, and wear performance. The epoxidation process resulted in nearly doubling the oxidative stability, as well as improving the thermal stability of the MO. Results showed that the EMO exhibited better lubricating properties than the MO, including lower friction and wear. To further improve the lubrication performance of the EMO, solid lubricant additives (SLAs) were incorporated in various concentrations. These SLAs were graphene nanoplatelets (GNP) and hexagonal boron nitride (hBN). The GNP and hBN nano lubricants reduced friction by 31% and 13% compared to the EMO. The same nano lubricants also lowered wear by 73% and 51% relative to the EMO. The underlying mechanisms behind the improvement in the friction and wear performance were discussed. The EMO can be considered as a suitable base stock for renewable and sustainable energy applications.

Microwave-assisted synthesis of oleic acid-capped silver nanoparticles as lubricant additives

Recently, metal nanoparticles have been studied extensively as lubricant additives. Owning to their nanometer size, the nanoparticles can fill micro defects on contacting surfaces, acting as repairing agents. In this work, we describe a simple and fast method to fabricate monodisperse silver nanoparticles using oleic acid as a capping agent. In particular, silver nitrate was reduced by oleylamine in the oleic acid medium using acetonitrile as a co-solvent, and the reaction was heated by a microwave source. Results showed that the particle size was greatly affected by varying the reductant concentration. The average diameter of synthesized nanoparticles ranges from 3.0 nm to 4.0 nm at optimum conditions. The dispersibility in the oil of the product is attributed to the long-chain alkyl from fatty acid grafted on the surface layer, which constitutes about 21% of the weight of the nanoparticles as determined by thermogravimetric analysis.

Adhesion and structure of lubricant films: Molecular simulations of amine-based organic additives in base oil at a model of steel surface

Wear mitigation in gears and rolling bearings lengthens the service life of machines and contributes to the achievement of a more sustainable society. Organic additives form protective films on rubbing steel surfaces of mechanical contacts that can mitigate wear significantly. However, wear prevention requires the design of new additives for lubricants that are environmentally friendly. Molecular simulations are employed to investigate the effect of the base oil on the adsorption, the lubricant adhesion, and structural properties of a promising organic additive (N,N - Bis(4-aminobutyl) oleylamine). Results are compared with oleylamine. They suggest better performances for the promising organic additive. Overall, findings further support the fact that additives with polar head groups with aminoalkyl branches reduce wear efficiently in mechanical contacts.

Tribological Properties of h-BN, Ag and MgO Nanostructures as Lubricant Additives in Vegetable Oils

There exists an ever-growing need for sustainable engineering solutions to improve emission control and the energy efficiency of tribosystems. This study examines the tribological properties of two environmentally friendly vegetable fluids, soybean and sunflower oil, with the addition of three non-toxic nanostructures (h-BN, silver and MgO) at different concentrations. It was found that nanostructures added to vegetable oils at specific concentrations can exhibit good friction reduction and wear preventive properties. The addition of h-BN nanosheets in sunflower oil decreased the coefficient of friction and the wear damage, as measured by the wear scar diameter. Silver and magnesium oxide nanoparticles further reduced the friction and wear, respectively. In addition to the tribological testing of the samples, investigations were performed using an optical microscope, SEM and EDX to elucidate the mechanisms that may have led to the observed friction reduction and wear-preventive properties of different nanostructure additives. The thermophysical properties of the samples were also measured. It was found that the thermal conductivity of both base oils could be enhanced by 24% when using h-BN at 0.25 wt% concentration.

Improving physicochemical and tribological characteristics of bio-lubricants using carbon-based hybrid nanomaterials modified by tertiary-butyl-hydroquinone

Vegetable oils are being increasingly studied in tribology due to their environmental benefits. This study investigates the physicochemical and tribological properties of carbon black/silver (CB/Ag) hybrid nanomaterials modified by tertiary-butylhydroquinone (TBHQ) as lubricant additives. The composition of the tribolayer formed were characterized using an FE-SEM, 3D surface profilometer, and XPS analysis. The results reveal a substantial decrease in the coefficient of friction (COF) value for the hybrid nanolubricant, with an approximate 31% reduction compared to the baseline oil. Finally, the characterization of worn surfaces strongly supports the noteworthy improvement in friction performance, primarily ascribed to the synergistic effects of CB, Ag nanoparticles, and TBHQ antioxidant surfactants. This study affirms that TBHQ-modified CB/Ag hybrid nanoparticles serve as eco-friendly lubricant additives.

Sliding tribological properties of nano-sized ceramic particles as oil-based lubricant additives

The present research investigated the lubricating performance of ZnO, SiO2, and WS2 nanoparticles as oil additives applied on steel frictional pairs. The study consisted of two stages. In first stage, the lubricating properties of nanofluids were examined using the various nanoparticle concentrations. It was obtained that the 3wt% ZnO, 5wt% SiO2, and 3wt% WS2 nanofluids showed the best performance. In second stage, an orthogonal test matrix was designed to understand the influences of load, sliding frequency and surface roughness on the lubricating behavior of the nanofluids. It was found that the frequency and load had the most significant effects on the friction reduction and anti-wear properties of ZnO, SiO2, and WS2 nanofluids. By using scanning electron microscopy and energy dispersive X-ray spectroscopy for potential mechanisms. It was found that the nanoparticles could be physically embedded, and adhered to the worn areas to form tribo-films resulting in improved tribological performance.

Удосконалення механізму притирання вільним абразивом за допомогою використання силікатного складу

The results of an experimental study are presented that explain and confirm the mechanism of lapping friction surfaces with a silicate abrasive composition.
 It is shown that the stability of the silicate lapping paste over time can be achieved by introducing ferric trichloride (FeCl3), which in this case is a thickener of liquid glass and also has high hygroscopic properties. The adhesive properties of the silicate paste are improved by the addition of lubricant 1-13. This grease was chosen due to its water solubility. To increase the abrasive ability of the silicate paste, an abrasive powder was introduced. 
 It was found that the lapping performance of the silicate composition and the quality of surfaces are higher than when treated with the «KT» paste, which is currently used for lapping automobile engine valves. Based on the results of the study, the mechanism of lapping friction surfaces with a silicate paste is presented. The mutual movement of the surfaces results in cutting and scratching of the highest peaks of the bumps by the abrasive grains. When silicon oxide (SiO2) is added to the abrasive material, its particles are coated with silicon oxide. This is because liquid glass solutions have a high adhesive force and low surface tension. At the points of contact between the abrasive particles, the temperature rises, and since there is SiO2 around the abrasive, when the latter enters the contact zone, amorphous silica (SiO2) is formed. Since the abrasive grains are coated with a silicon oxide film, SiO2 penetrates into the cavities of micro-irregularities and adheres to the surface under repeated exposure to the abrasive. Thus, the surface to be treated is saturated with silicon oxide, which leads to an increase in its quality after grinding with a silicate composition.
 It has been proven that high surface quality is formed by amorphous silica. To confirm this mechanism, chemical and X-ray spectral analyses of the samples were performed, which showed the presence of SiO2 on the treated surface and a "strong bond" of silicon compounds with the metal surface layer. 
 It was found that the high quality of the surface is also due to the shape of abrasive particles and wear products. It has been confirmed that with the variable movement of surfaces relative to each other, abrasive grains take on a new position each time. At the same time, they are worn from all sides and acquire a rounded shape, and are simultaneously enveloped by a SiO2 foil.

Effect of PAO-4 and MoDTC + ZnDTP oil additive lubricants on the tribological performance of novel tetrahedral amorphous carbon (ta-C) coatings

This study was carried out to assess the effect of PAO-4 and mineral oil mixed with MoDTC and ZnDTP on the tribological performance of novel tetrahedral-amorphous-carbon (ta-C) coatings namely P:ta-C, and M:ta-C, were analysed using the Pin-on-Disk Tribo-tester with a fixed normal load, temperature, sliding distance and speed of 20 N, 80 °C, 250 m and 0.068 ms−1 for 60 min, respectively. The C:ta-C, P:ta-C, and M:ta-C showed excellent wear resistance when lubricated with MoDTC + ZnDTP. The formation of weak Zn-derived tribofilm on the P:ta-C coating contributed to the strong wear resistance and reduced friction coefficient. Moreover, the passive transfer of ferrous compounds from the SUJ2 disk induced the development of weak Zn-derived tribofilm on the P:ta-C and M:ta-C.

The Effect of Carbon Structure of DLC Coatings on Friction Characteristics of MoDTC-Derived Tribofilm by Using an In Situ Reflectance Spectroscopy

In this study, six types of DLC coatings were prepared, featuring different carbon structures (including amorphous ta-C coatings and GNC coatings with nanocrystallites) and different doped Ta amounts, to investigate friction characteristics. The results of friction tests with MoDTC-added lubricant revealed a consistent trend: DLC coatings with a higher ID/IG ratio exhibited lower friction coefficients. In addition, in situ observations using reflectance spectroscopy highlighted that the tribofilm formed on DLC coatings with a higher ID/IG ratio maintained a higher MoS2/(MoS2+MoO3)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{MoS}}}_{2}/({{\ ext{MoS}}}_{2}+{{\ ext{MoO}}}_{3})$$\\end{document} ratio, which exhibited a strong correlation with the friction coefficient. Measurements of a work function of each DLC coating indicated that those with a higher ID/IG ratio had a higher work function, suggesting the inclusion of a larger amount of graphite structure defects. These active defects in the graphite structure were deemed responsible for enhancing the friction reduction effect of MoDTC. The outcomes of this study propose a material design approach for DLC coatings that amplifies the effectiveness of lubricant additives in friction reduction.Graphical abstract

Synergistic effect of MXene and PTFE with multi-structure as lubricant additives for tribological applications

Nanomaterials play an important role in reducing friction and wear when used as lubricating additives. Due to synergistic effects, nanocomposites often have superior lubrication properties than individual materials. Therefore, based on the structural differences between MXene and phenolic resin modified polytetrafluoroethylene (mPTFE), MXene@mPTFE composites with multiple heterogeneous structures are designed and constructed. As expected, the synergistic effect of layered MXene and mPTFE nanoparticles endows MXene@mPTFE excellent tribological performance. Under the action of shear force, mPTFE nanoparticles accelerate the interlayer slip between MXene nanosheets, and mPTFE nanoparticles with high hardness and thermal stability act as ball bearings to improve the extreme pressure characteristics of the oil. Compared to base oil (PAO-6), the coefficient of friction (COF) decreased from 0.644 to 0.111, the wear volume decreased by 92.7 %, and the bearing capacity increased to 750 N. This study provides new implications for the development of nanolubricant additives.

Effect of 2D Cu-MOFs modified carbon spheres nanoparticles as an environmentally friendly lubricating additive on tribological properties

As a nanoscale carbon material, carbon spheres (CS) are expected to achieve ideal lubrication performance by reducing direct contact between friction pairs and bearing loads. In this work, 2D Cu-MOFs surface modified (CS@Cu(BDC)) CS was added to the base oil, which exhibited a remarkable reduction in friction coefficient and wear rate (62.2%, 33.9%), the width of the friction pair wear marks was decreased by 30.8% relative to the base oil. The improvement in performance can be attributed to the polishing, repairing, filling and tribo-film forming effects of CS@Cu(BDC). This work provided an effective strategy for diversifying the surface structure of CS and opened new avenues for the development of a new generation of green and efficient lubricant additives.

Preparation and tribological property of MoS2@PDA@POSS core-shell-shell/Epoxy composite lubricating coating with good humidity adaptability

In this work, a humidity-adaptive additive of MoS2@PDA@POSS with core-shell-shell structure was designed and fabricated in the presence of polydopamine (PDA) interlayer. Then the composite coating of MoS2@PDA@POSS/Epoxy was prepared by introducing this additive into epoxy matrix, and its tribological properties under air and humid environments were subsequently evaluated in detail. Specially, the friction coefficient of MoS2 @PDA@POSS/Epoxy coating under high humid environment remained stable below 0.25, while its volume wear rate reduced by 91.91% compared to MoS2/Epoxy coating, and the humidity-adaptive response mechanism mainly depends on the improved mechanical properties, the alleviating effect on MoS2 oxidation, and the formation of transfer film. This work establishes a promising platform for the design and application of novel high-performance lubricating additives.

Tribological properties of two-dimensional nanochains in water controlled by a magnetic field with various alignment directions

Nanoparticles are extensively utilized as effective lubrication additives. In a novel approach, one-dimensional nanoparticles undergo self-assembly, transforming into two-dimensional nanochains for use as additives, thereby enabling varied lubrication effects. We involved synthesizing Fe3O4 nanoparticles via a solvothermal method, followed by their self-assembly into magnetic Fe3O4@SiO2 nanochains under a magnetic field. These NCs, measuring 57.8 µm in length and 0.2 µm in diameter, were dispersed in deionized water. This study explored the influence of various orientations on the tribological properties of the lubricant through the manipulation of nanochains’ alignment using a magnetic field. The results indicate a 48.51% reduction in coefficient of friction and a 73.56% decrease in wear rate when the NCs were aligned perpendicular to the direction of friction.

Surface-Modified LDH Nanosheets with High Dispersibility in Oil for Friction and Wear Reduction.

Surface and interfacial engineering of nanomaterials is essential for improving dispersion stability in liquids. In this study, we report that oleic acid (OA)- and stearic acid (SA)-functionalized layered double hydroxide (LDH) nanosheets as lubricant additives can achieve high dispersion and reduce friction and wear. LDH is a typical layered structure, and OA and SA are long-chain organic molecules that are not only compatible with base oils but also act as friction-reducing agents. The OA and SA molecules were branched onto ZnMgAl LDH nanosheets using dehydration condensation between the exposed OH groups on the surface of LDH and the COOH groups on the OA and SA molecules. Compared with that of the pristine ZnMgAl LDH, the dispersion of OA-ZnMgAl LDH and SA-ZnMgAl LDH was significantly improved. The surface-modified LDH exhibited superior tribological properties and great stability due to the synergistic lubrication effect between OA, SA, and LDH. Even at an ultralow concentration (0.15 wt %), the coefficient of friction and wear volume were reduced by ∼65 and ∼99%, respectively, compared to those of the base oil. Due to the green and simple synthesis method and excellent tribological properties, surface-functionalized LDH has enormous possibilities for future industrial applications.